I have a problem with my HRV that has me completely stumped. Moved into the house 6 months ago, and noticed from time to time that it smelled faintly like sewer gas inside. Made sure all the P traps had water, and never found the source. It wasn't until recently that we made the connection that when the HRV is on for a while, it smells like sewer! There is absolutely no sewer smell outside where the intake is. I pulled apart the inlet duct thinking something had somehow gotten in there and died, but no luck. (and it really does smell like sewer gas, not something rotting.) I put the HVR in recirculation mode, and the outlets still smell like sewer, so it's not something that it's drawing in from outside. Strangely enough, when I disconnect the supply side right at the HRV, I can't smell anything from the ductwork, but I can smell it coming from the HRV when the fan is on. When I open the HRV up, there is no smell inside. It's almost as if the smell was coming from the fan itself, which I know makes no sense. But assuming I'm wrong about that and it's not coming from the fan, how can I possibly be getting a sewer smell in the supply ducts? So much for pumping clean, fresh air into the house! I have radiant heating, so the ducts are only for HRV. HELP! It's getting cold and I was planning on relying more and more on my HRV instead of the bathroom fans.

 

How old is the unit?

How are the air filters?

Has the core been cleaned lately? (Some can be washed out)

The drain, is it going to the floor or tied to the house plumbing?

 

Jay, you are a genius. To answer your questions, the unit is less than 2 years old, and I have pulled out the filters/core and cleaned them, which led me down a rabbit hole that I'll talk about in a second. It was your last question that made the light bulb go off in my head. I have been fighting with this for hours, trying to find the problem. I took out the core to clean it and on a whim, ran it without the core (which just makes the HRV a big circulator) and noticed that the smell went away! How can an aluminum core possibly emit a sewer smell? But sure enough, as soon as I put it back in, the smell came back. I was about to seal it in a plastic bag for awhile to see if I could concentrate the smell and confirm it was the core when I read your post. Then I realized I have not accounted for the drains at all. The drains come off, connect to a T, and then a common line runs to Y in a stub coming out of the garage slab. The other side of the Y connects to the output of my water softener. I don't know if there is a trap below the stub or not, but I suspect it runs straight to the sewer pipe, and when the core is in the HRV, it seals the supply side so it creates a vacuum, drawing air in through the common drain line. I'll leave it off the drain pipe for a while to make sure, but for now, it seems that the drain was the source of my problems. If so, I'll just let it drain to the floor
That leads me to another question. Since it was drawing air in through my drain, does that mean my system is out of balance, since the drains should theoretically be neutral? Also, as I was running it with the core out, it occurred to me that the should also create a neutral balance, so can I run it that way to make sure my system is in balance? (run it without the core, and check the supply and return vents outside; if neither is sucking or blowing air, then it should be balanced, right?) I've got dampers on the supply and return lines leading up to the HRV, should I adjust them so that I have a slight positive pressure? Thanks for your help!

 

The P trap on your system, is it a clear vinyl hose that you can see the water level?

not sure what brand you got, and where the drain is sitting at inside of the unit?

 

There is no P trap in the HRV system. The drains on each side (supply and return), connect to a common T via clear vinyl tubing, then a single clear vinyl tube runs to the stubbed out sewer pipe. The vinyl tube has a hose fitting at the end, which is screwed to the Y at the fitting at the sewer pipe. If I just let the vinyl tube drain to the floor and cap the Y, I should be OK.

 

I take it you have a LifeBreath system?

Move the T upwards to make a trap for the water.

 

Will do...thanks for the tip. Do you have any thoughts on balancing the system?

 

You most likely don't have the tools to measure the pressure.

But once you get this T turned up enough to make a water trap, you will see the water go higher on side vs the other, that is normal.. How ever, if you see that the water is sucked out, then we have a balance issue.